Yttrium fluoride spray material, yttrium oxyfluoride-deposited article, and making methods

ABSTRACT

An yttrium fluoride spray material contains Y 5 O 4 F 7  and YF 3 , and has an average particle size of 10-60 μm and a bulk density of 1.2-2.5 g/cm 3 . The Y 5 O 4 F 7  and YF 3  in the yttrium fluoride spray material consist of 30 to 90% by weight of Y 5 O 4 F 7  and the balance of YF 3 . A sprayed coating of yttrium oxyfluoride is obtained by atmospheric plasma spraying of the spray material.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 15/331,324filed on Oct. 21, 2016, now U.S. Pat. No. 10,538,836, and is based uponand claims the benefits of priority from Japanese Patent Application No.2015-208616 filed on Oct. 23, 2015, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

This invention relates to an yttrium oxyfluoride-deposited article foruse in the plasma etching step of the semiconductor device fabricationprocess, an yttrium fluoride spray material for use in making thearticle, and making methods thereof.

BACKGROUND ART

In the etching step of the semiconductor device fabrication process,treatment is carried out in a corrosive halogen-base gas plasmaatmosphere. While the etching system includes parts which are exposed tothe halogen-base gas plasma, parts having coatings formed by sprayingyttrium oxide or yttrium fluoride to the surface of metallic aluminum oraluminum oxide ceramic substrates are known to be fully corrosionresistant and used in practice. See Patent Documents 1 to 4. Typicalcorrosive halogen-base gases used in the process for manufacturingsemiconductor devices are fluorine-base gases such as SF₆, CF₄, CHF₃,ClF₃ and HF and chlorine-base gases such as Cl₂, BCl₃ and HCl.

Yttrium oxide-deposited parts obtained by atmospheric plasma spraying ofyttrium oxide suffer from few technical problems and have long beenutilized as semiconductor-related spray members. On the other hand,yttrium fluoride-sprayed coatings suffer from technical problems despiteexcellent corrosion resistance. For example, during atmospheric plasmaspraying of yttrium fluoride, the yttrium fluoride is passed through aflame of 3,000° C. or higher and melted therein, whereby the fluoridecan be decomposed. Then the coating partially contains a mixture offluoride and oxide. For this reason, the practical utilization ofyttrium fluoride-deposited parts is delayed as compared with theoxide-deposited parts.

When yttrium oxide-deposited parts are used in the etching process withfluorine gas, there arises the problem that the etching process becomesunstable because outermost yttrium oxide reacts with a fluorine-base gasat the initial of the process, and so the fluorine-base gasconcentration within the equipment varies. This problem is known as“process shift.” The replacement by yttrium fluoride-deposited parts isunder consideration. However, yttrium fluoride tends to have slightlylow corrosion resistance in a halogen-base gas plasma atmosphere, ascompared with yttrium oxide. In addition, yttrium fluoride sprayedcoatings have many crevices on their surface and release many particles,as compared with yttrium oxide sprayed coatings.

It is thus believed that yttrium oxyfluoride having characteristics ofboth yttrium oxide and yttrium fluoride is more advantageous. PatentDocument 5 discloses such an attempt. While yttriumoxyfluoride-deposited parts are prepared by standard atmospheric plasmaspraying of yttrium oxyfluoride, the deposition of yttrium oxyfluoridesprayed coatings is difficult because a compositional shift of fluorinedepletion and oxygen enrichment occurs due to oxidation.

CITATION LIST

Patent Document 1: JP 3672833 (U.S. Pat. No. 6,576,354)

Patent Document 2: JP 4905697 (U.S. Pat. No. 7,655,328)

Patent Document 3: JP 3523222 (U.S. Pat. No. 6,685,991)

Patent Document 4: JP 3894313 (U.S. Pat. No. 7,462,407)

Patent Document 5: JP 5396672 (US 2015/0096462)

SUMMARY OF INVENTION

An object of the invention is to provide an yttrium fluoride spraymaterial which ensures stable formation of an yttrium oxyfluoridesprayed coating by atmospheric plasma spraying, the yttrium oxyfluoridesprayed coating being minimized in process shift and particle release ascompared with conventional sprayed coatings of yttrium oxide and yttriumfluoride; an yttrium oxyfluoride-deposited article obtained by sprayingthe yttrium spray material; and methods for preparing the spray materialand article.

The inventors have found that an yttrium fluoride spray materialconsisting essentially of 30 to 90% by weight of Y₅O₄F₇ and the balanceof YF₃ is effective for compensating for any compositional shift duringatmospheric plasma spraying.

A first embodiment of the invention is an yttrium fluoride spraymaterial comprising Y₅O₄F₇ and YF₃, the Y₅O₄F₇ and YF₃ consisting of 30to 90% by weight of Y₅O₄F₇ and the balance of YF₃, and spray materialhaving an average particle size of 10 to 60 μm and a bulk density of 1.2to 2.5 g/cm³.

A second embodiment of the invention is a method for preparing theyttrium fluoride spray material defined above, comprising the steps ofmixing 10 to 50% by weight of yttrium oxide having an average particlesize of 0.01 to 3 μm with the balance of an ammonium fluoride complexsalt of formula: (YF₃)₃NH₄F·H₂O, having an average particle size of 0.01to 3 μm, granulating and firing.

A third embodiment of the invention is an yttrium-deposited articlecomprising a substrate and a coating sprayed thereon, the sprayedcoating containing at least one yttrium oxyfluoride selected from thegroup consisting of YOF, Y₅O₄F₇, and Y₇O₆F₉.

A fourth embodiment of the invention is a method for preparing anyttrium-deposited article, comprising the step of atmospheric plasmaspraying the yttrium fluoride spray material defined above to asubstrate to form a sprayed coating containing at least one yttriumoxyfluoride selected from the group consisting of YOF, Y₅O₄F₇, andY₇O₆F₉ thereon.

Advantageous Effects of Invention

The yttrium fluoride spray material of the invention ensures stableformation of an yttrium oxyfluoride sprayed coating by atmosphericplasma spraying.

DESCRIPTION OF PREFERRED EMBODIMENTS

The yttrium fluoride spray material of the invention contains yttriumoxyfluoride (Y₅O₄F₇) along with yttrium fluoride (YF₃). The yttriumfluoride spray material is preferably free of yttrium oxide (Y₂O₃). Forexample, an yttrium fluoride spray material in which yttrium oxyfluoride(Y₅O₄F₇) and yttrium fluoride (YF₃), especially, only both of Y₅O₄F₇ andYF₃ are detected as crystalline phases by X-ray diffraction ispreferable. The yttrium fluoride spray material contains 30 to 90%,preferably 60 to 80% by weight of Y₅O₄F₇ and the balance of YF₃ withrespect to the total of Y₅O₄F₇ and YF₃. The spray material may containsa small amount of other crystalline phases such as YOF, however, thetotal of Y₅O₄F₇ and YF₃ is preferably at least 90 wt %. Particularly,the spray material consisting essentially of Y₅O₄F₇ and YF₃ is morepreferable. The yttrium fluoride spray material of the invention has anaverage particle size of 10 to 60 μm, preferably 25 to 45 μm and a bulkdensity of 1.2 to 2.5 g/cm³, preferably 1.3 to 2.0 g/cm³.

When a sprayed coating is formed by atmospheric plasma spraying of anyttrium fluoride spray material, the sprayed coating has an oxygenconcentration which is increased and a fluorine concentration which isdecreased, indicating partial oxidation of the spray material. Thisyttrium fluoride spray material is suited to form a stable yttriumoxyfluoride coating by atmospheric plasma spraying. From the standpointof compensating for any compositional shift during atmospheric plasmaspraying, an yttrium fluoride spray material consisting essentially of30 to 90% by weight of Y₅O₄F₇ and the balance of YF₃ is effective, withrespect to the total of Y₅O₄F₇ and YF₃.

Preferably the thermal spray powder material is free-flowing andcomposed of particles of spherical shape for thermal spraying. When aspray material is fed into a flame for thermal spraying, a poor flow maycause cumbersome operation such as clogging of a feed tube. To ensure asmooth flow, the spray material should preferably take the form ofspherical particles, specifically having an aspect ratio of up to 2,more specifically up to 1.5. As used herein, the term “aspect ratio” isan index of particle configuration and refers to the ratio of length tobreadth of a particle.

An angle of repose is an index of flow. A smaller angle of reposeindicates better flow. The spray material preferably has an angle ofrepose of up to 45°, more preferably up to 40°. The angle of repose isdetermined by particle shape, particle size, particle size distribution,and bulk density. In order that the spray material have a small angle ofrepose, it should preferably have spherical shape, an average particlesize of at least 10 μm, and a sharp particle size distribution.

The spray material in particulate form preferably has an averageparticle size D50 of from 10 μm to 60 μm. The average particle size D50is determined by laser light diffractometry. If the particle size ofspray material is too small, such particles may evaporate off the flame,resulting in a low yield of spraying. If the particle size of spraymaterial is too large, such particles may not be completely melted inthe flame, resulting in a sprayed coating of poor quality. It isimportant that spray material particles obtained by granulation besolid, i.e., filled to the interior (or free of voids), for the reasonthat solid particles are unbreakable and stable during handling, and thetendency that voided particles trap undesirable gas component in theirvoids is avoided.

Now the method for preparing the yttrium fluoride spray material isdescribed. For example, 10 to 50% by weight of yttrium oxide having anaverage particle size of 0.01 to 3 μm is mixed with the balance of theammonium fluoride complex salt of formula: (YF₃)₃NH₄F·H₂O having anaverage particle size of 0.01 to 3 μm, and optionally with adding abinder. Organic compounds are preferable as the binder. Examples of thebinder include organic compound consisting of carbon, hydrogen andoxygen or carbon, hydrogen, oxygen and nitrogen, such as carboxymethylcellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl pyrrolidone(PVP). The mixture is granulated and fired, yielding the desired yttriumfluoride spray material. The method for synthesizing the ammoniumfluoride complex salt is described. For example, an yttrium nitratesolution is mixed with an acidic ammonium fluoride solution at atemperature of 0° C. to 80° C., preferably 40° C. to 70° C., from whicha white precipitate crystallizes out. The precipitate is filtered,washed with water, and dried. It is identified to be an ammoniumfluoride complex salt of formula: (YF₃)₃NH₄F·H₂O by X-ray diffractometryanalysis.

The firing step may be performed in vacuum or an inert gas atmosphere ata temperature of 600° C. to 1,000° C., preferably 700° C. to 900° C. for1 to 12 hours, preferably 2 to 5 hours.

Thermal spraying of the yttrium fluoride spray material to a substrateis desirably performed under atmospheric pressure (normal pressure) orreduced pressure. Although the plasma gas is not particularly limited,examples of the plasma gas include nitrogen/hydrogen, argon/hydrogen,argon/helium, argon/nitrogen, argon alone, and nitrogen gas alone, withargon/nitrogen being preferred.

Examples of the substrate subject to thermal spraying include, but arenot limited to, substrates of stainless steel, aluminum, nickel,chromium, zinc, and alloys thereof, alumina, aluminum nitride, siliconnitride, silicon carbide, and quartz glass, which serve as components ofthe semiconductor fabrication equipment. The sprayed coating typicallyhas a thickness of 50 to 500 μm. The conditions under which the spraymaterial is thermally sprayed are not particularly limited and may bedetermined as appropriate depending on the identity of substrate, aparticular composition of the spray material and sprayed coating, and aparticular application of the sprayed article.

According to the atmospheric plasma spraying of the yttrium fluoridespray material of the invention, a sprayed coating is formed and anyttrium oxyfluoride-deposited article including a substrate and asprayed coating formed thereon is obtained. The sprayed coating containsat least one yttrium oxyfluoride selected from the group consisting ofYOF, Y₅O₄F₇, and Y₇O₆F₉, particularly, YOF, or YOF and Y₅O₄F₇. Thesprayed coating is preferably free of yttrium oxide (Y₂O₃) and desirablycontains only yttrium oxyfluoride.

A typical example of argon/hydrogen plasma spraying is atmosphericplasma spraying using a gas mixture of 40 L/min of argon and 5 L/min ofhydrogen with air as an ambient gas. The thermal spraying conditionsincluding a spray distance, current value, voltage value, and the feedrates of argon and hydrogen gases may be determined as appropriatedepending on a particular application of the sprayed component or thelike. A powder hopper is charged with a predetermined amount of spraymaterial, which is fed with the aid of a carrier gas (typically argon)through a powder hose to the front end of the plasma spraying gun. Whilethe spray material is continuously fed into the plasma flame, it iscompletely melted and liquefied, forming a liquid flame under theimpetus of plasma jet. The liquid flame impinges against a substrate,whereupon molten particles are fused, solidified, and deposited thereon.On this principle, an yttrium oxyfluoride-deposited article (sprayedmember) can be manufactured by forming yttrium oxyfluoride sprayedcoating within a predetermined coating region on the substrate by movingthe flame from right to left and/or up and down with a robot or humanarm.

The sprayed article is evaluated for particle release, for example, by asimple particle test. The deposited article is immersed in apredetermined volume of pure water for a predetermined time underultrasonic agitation. Nitric acid is added to the collected immersionsolution to dissolve particles. The yttrium content of the solution ismeasured by inductively coupled plasma (ICP) spectroscopy. A loweryttrium content indicates fewer particles.

EXAMPLE

Examples are given below by way of illustration and not by way oflimitation. In Table, wt % is percent by weight.

Reference Example 1

Preparation of Ammonium Fluoride Complex Salt

A 1 mol/L yttrium nitrate solution, 1 L, was heated at 50° C. and mixedwith 1 L of a 1 mol/L acidic ammonium fluoride solution at 50° C. forabout 30 minutes with stirring. A white precipitate crystallized out.The precipitate was filtered, washed with water and dried. On X-raydiffractometry analysis, it was identified to be an ammonium fluoridecomplex salt of formula: (YF₃)₃NH₄F·H₂O. It had an average particle sizeof 0.7 μm as measured by laser light diffractometry.

Examples 1 to 5 and Comparative Examples 1 and 2

Preparation of Spray Powder (Spray Material)

A spray powder material was obtained by mixing predetermined amounts ofingredients to form a mix as shown in Table 1, dispersing the mix inwater, with adding a binder in Examples 1 to 4 and Comparative Examples1 and 2 or without adding a binder in Example 5, shown in Table 1 toform a slurry, granulating by means of a spray dryer, and firing underthe conditions shown in Table 1. The resulting spray powder wasidentified and measured for crystal structure, particle sizedistribution, bulk density, angle of repose, and yttrium, fluorine,oxygen, carbon and nitrogen concentrations. The results are shown inTable 1. Notably, the identification was performed by X-raydiffractometry, the particle size distribution was measured by laserlight diffractometry, the bulk density and angle of repose were measuredby a powder tester, yttrium concentration was analyzed byethylenediamine tetraacetic acid (EDTA) titration method of dissolvedsamples, the fluorine concentration was analyzed by dissolution ionchromatography, and the oxygen, carbon and nitrogen concentrations wereanalyzed by the infrared (IR) method after combustion. In each ofExamples 1-5 and Comparative Examples 1 and 2, carbon and nitrogen werenot detected, i.e., carbon and nitrogen concentrations were 0 wt %,respectively. Each of contents of the yttrium compound components wasdetermined as follows. In Examples 1 to 5 and Comparative Example 1,Y₅O₄F₇ content was calculated based on the oxygen concentration, and YF₃content was calculated as the balance. In Comparative Example 2, contentof each of three substances (crystalline phases), which was identifiedby X-ray diffractometry, was calculated from scale factors of thecrystalline phases.

Preparation of Sprayed Article

Each of the spray powder materials in Examples 1 to 5 and ComparativeExamples 1 and 2 was deposited onto an aluminum substrate by atmosphericplasma spraying using a gas mixture of 40 L/min of argon and 5 L/min ofhydrogen with air as an ambient gas. The deposited article (sprayedmember) had a sprayed coating of about 200 μm thick. The sprayed coatingwas scraped off the coated article. The sprayed coating was identifiedby X-ray diffractometry, and analyzed for yttrium concentration byethylenediamine tetraacetic acid (EDTA) titration method of dissolvedsamples, fluorine concentration by dissolution ion chromatography, andoxygen concentrations by the combustion IR method. The results are shownin Table 2.

In Examples 1 to 5, the yttrium fluoride spray material which had beenprepared by mixing 10 to 50% by weight of yttrium oxide with the balanceof ammonium fluoride complex salt of (YF₃)₃NH₄F·H₂O, granulating andfiring was a mixture of 30 to 90% by weight of Y₅O₄F₇ and the balance ofYF₃. When the spray material was deposited onto an aluminum substrate byatmospheric plasma spraying using a gas mixture of 40 L/min of argon and5 L/min of hydrogen with air as an ambient gas, the sprayed coatingconsisted of at least one yttrium oxyfluoride selected from among YOF,Y₅O₄F₇, and Y₇O₆F₉.

In Comparative Examples 1 and 2, the yttrium fluoride spray material wasprepared by mixing predetermined amounts of yttrium oxide (Y₂O₃) andyttrium fluoride (YF₃), granulating and firing. When the spray materialwas deposited onto an aluminum substrate by atmospheric plasma sprayingusing a gas mixture of 40 L/min of argon and 5 L/min of hydrogen withair as an ambient gas and deposited article was obtained, the sprayedcoating contained Y₂O₃.

The deposited articles of Examples 1 to 5 and Comparative Examples 1 and2 were washed with running pure water at a flow rate of 100 L/hr beforethey were immersed in 10 L of pure water for 10 minutes under ultrasonicagitation. To the collected immersion solution, 100 mL of 2 mol/L nitricacid was added. The yttrium content of the solution was measured by ICP.The results are shown in Table 3.

TABLE 1 Comparative Example Example 1 2 3 4 5 1 2 Ingredients, Y₂O₃ (D50= 0.3 μm) particle size, 20 wt % 30 wt % 40 wt % 50 wt % 20 wt % 10 wt %50 wt % and mixing ratio (YF₃)₃NH₄FH₂O (D50 = 0.7 μm) YF₃ (D50 = 1.4 μm)80 wt % 70 wt % 60 wt % 50 wt % 80 wt % 90 wt % 50 wt % Granulation Mix25 wt % 25 wt % 25 wt % 25 wt % 25 wt % 25 wt % 25 wt % conditionsBinder* CMC CMC PVA PVP none CMC CMC  8 wt %  8 wt %  8 wt %  8 wt %  8wt %  8 wt % Firing Atmo- N₂ vacuum N₂ N₂ N₂ N₂ N₂ conditions sphereTemper- 800° C. 900° C. 900° C. 800° C. 800° C. 800° C. 800° C. atureAnalysis of spray powder Particle D10, μm 23 18 25 21 23 22 23 size D50,μm 37 28 38 33 37 37 34 distribution D90, μm 54 48 65 47 54 59 64 Bulkdensity, g/cm³ 1.3 1.6 1.7 1.3 1.3 1.3 1.4 Angle of repose, ° 39 38 3639 39 42 41 Y concentration, wt % 66.9 68.4 67.4 67.9 66.9 65.6 72.7 Fconcentration, wt % 28.8 24.5 24.6 22.9 28.8 32.1 16.4 O concentration,wt % 4.3 7.1 8.0 9.2 4.3 2.3 10.9 X-ray diffraction Y₅O₄F₇ Y₅O₄F₇ Y₅O₄F₇Y₅O₄F₇ Y₅O₄F₇ Y₅O₄F₇ Y₅O₄F₇ analysis 43 wt % 71 wt % 80 wt % 92 wt % 43wt % 23 wt % 87 wt % YF₃ YF₃ YF₃ YF₃ YF₃ YF₃ YF₃ 57 wt % 29 wt % 20 wt % 8 wt % 57 wt % 77 wt %  9 wt % Y₂O₃  4 wt % *CMC: carboxymethylcellulose, PVA: polyvinyl alcohol, PVP: polyvinyl pyrrolidone

TABLE 2 Analysis Comparative of sprayed Example Example coating 1 2 3 45 1 2 Y concen- 66 69.6 72.4 71.5 66 66 73 tration, wt % F concen- 26.721.4 16.6 15 26.7 30.4 14.3 tration, wt % O concen- 7.3 9 11 13.5 7.33.6 12.7 tration, wt % X-ray Y₅O₄F₇ Y₅O₄F₇ Y₅O₄F₇ YOF Y₅O₄F₇ Y₅O₄F₇ YOFdiffraction YOF YOF YOF YOF YF₃ Y₂O₃ analysis Y₂O₃

TABLE 3 Comparative Simple particle Example Example test 1 2 3 4 5 1 2 Yconcentration, 3 5 7 10 3 20 30 mg/L

Japanese Patent Application No. 2015-208616 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A method for preparing a spray materialcomprising Y₅O₄F₇ and YF₃, the Y₅O₄F₇ and YF₃ consisting of 30 to 71% byweight of Y₅O₄F₇ and the balance 29 to 70% by weight of YF₃, the spraymaterial having an average particle size of 10 to 60 μm and a bulkdensity of 1.2 to 2.5 g/cm³, the method comprising the steps of: mixing10 to 50% by weight of yttrium oxide having an average particle size of0.01 to 3 •m with the balance of an ammonium fluoride complex salt offormula: (YF₃)₃NH₄F·H₂O having an average particle size of 0.01 to 3 •m,and granulating and firing the mixture.
 2. The method of claim 1 whereinin the mixing step, 10 to 40% by weight of yttrium oxide is mixed withthe balance of said ammonium fluoride complex salt.
 3. The method ofclaim 1 wherein the spray material is free of Y₂O₃.
 4. The method ofclaim 1 wherein the total of Y₅O₄F₇ and YF₃ contained in the spraymaterial is at least 90 wt %.
 5. The method of claim 1 wherein the spraymaterial has an average particle size of 33 to 60 •m.
 6. The method ofclaim 1 wherein the spray material has an angle of repose of up to 45°.